Updated, 7:24 p.m.: As of the end of the day, McCaskill says 53 senators have signed the letter.

Sen. Claire McCaskillClaire McCaskillMattis rips Pentagon officials for M wasted on Afghanistan camouflage Pentagon to address M spent on untested Afghan camouflage: report Federal Election Commission must not shy away from Russia probe MORE (D-Mo.) said Wednesday she has half the Senate on board with her effort to end senators' anonymous holds on nominations.

McCaskill said she now had 50 senators who had signed the letter she has been circulating pledging to end the use of the practice, in which one senator can object, without giving his or her name, to any nominee moving forward.

McCaskill tweeted Wednesday:


Now have 50 signatures on End the Secret Hold letter.More work on it today.Rules being broken by failure of Rs to reveal who's holding noms.

McCaskill said, too, in a conference call with Missouri reporters Wednesday that she's hopeful she can win a 60-vote, filibuster-proof majority on reform.

"We've crossed the majority -- we haven't gotten to 60, yet I'm feeling confident that we will get to 60," she said.

The Missouri centrist has been leading the charge against the practice, arguing it has been used to some effect by Republicans in the minority to stall or stop President Barack ObamaBarack ObamaTrump considers naming Yellen or Cohn to lead the Fed West Wing to empty out for August construction Ex-CIA chief: Trump’s Boy Scout speech felt like ‘third world authoritarian's youth rally’ MORE's nominees.

Senate Majority Leader Harry ReidHarry ReidConservative Senate candidate calls on GOP to end filibuster Ex-Reid aide: McConnell's 'original sin' was casting ObamaCare as 'partisan, socialist takeover' GOP faces growing demographic nightmare in West MORE (D-Nev.) railed against the practice of secret holds on Tuesday, suggesting the matter might be referred to the Senate Ethics Committee at some point.

Updated at 12:58 p.m.